This invention relates to improving the solid/liquid boundary definition in a welding process viewed by a vision sensor, especially by an arc welding torch having an integral puddle view optical system.
Recent work on vision guided tungsten inert gas (TIG) welding supports the premise that weld quality is related to the physical shape and size of the molten weld pool under the welding electrode of the torch as it traverses its prescribed path of travel. The puddle, presently illuminated solely by the arc, is not well enough defined to allow its edge to be automatically determined by computer analysis. Tests with autogeneous welds, those using no filler wire material, produced flat weld pool surfaces with resultant seams that lay below the plate surface ("negative reinforcement"). The image formed was of a dark pool against a lighter surrounding surface. For welds with filler wire, the pool surface becomes convex and stands above the plate surface ("positive reinforcement"). Such a surface scatters the arc illumination resulting in a light gray pool image against a light gray surrounding surface. This type of image is not easily processed to yield the perimeter of the molten pool.
In allowed application Ser. No. 451,219, filed Dec. 20, 1982, now N. R. Corby, Jr., U.S. Pat. No. 4,491,719, "Light Pattern Projector Especially for Welding", it is disclosed that structured light patterns, for instance parallel laser stripes, imaged on the entrance of a coherent optical fiber bundle and passed through it to an exit lens assembly on the torch, are projected onto the workpiece and joint ahead of the weld puddle to provide navigation data, or onto the puddle itself to provide information on its shape, extent and position to control the welding process. The present inventors noted that the stripe cleanly delineated the solid/liquid pool boundary at the points where the stripe crossed the pool boundary; however, the perimeter of the pool was indistinct.